I've checked our reports, and it seems there are no reported cases about the issue of missing customer information and invoices in QuickBooks Online.
With this, let's get your mobile app up and running by resetting the QuickBooks Application. This is the same as clearing the cache from your web browser. Let me guide how:
For Android device:
From More Options, then select the Settings tab.
Choose the Refresh Data menu.
Go to the Help menu.
Select Reset App Data.
However, if the issue persists, let's uninstall and reinstall the app for a clean slate. For uninstalling the QBO app using the iOs device, you can touch and hold the app, then click the Delete app button. Nothing to worry about uninstalling the app because it won't delete the transactions and subscriptions you have.
Tap Settings on your phone.
Select Apps and Notifications, then locate the QBO app.